Light projecting method and device

ABSTRACT

A waveguide comprises a first surface and a second surface. The second surface comprises a first plurality of grating structures. The waveguide is configured to guide an in-coupled light beam to undergo total internal reflection between the first surface and the second surface. The grating structures are configured to disrupt the total internal reflection to cause at least a portion of the in-coupled light beam to couple out of the waveguide from the first surface, the portion of the in-coupled light beam coupled out of the waveguide forming out-coupled light beams. The waveguide further comprises a reflective layer disposed on the second surface and covering the first grating structures.

TECHNICAL FIELD

This disclosure relates to methods and devices for projecting light.

BACKGROUND

Light projecting technologies are essential for enabling severalimportant device functionalities. For example, structured lightprojecting is deployed in 3D camera modules of mobile phones forrecognizing facial features. The projected light reflects off the facialfeatures can be captured by a detector and analyzed by algorithms to“perceive” the topology of the face. Accordingly, authentication, emojigeneration, image capture orientation, and other various functionalitiescan be designed based on inputs of the facial feature recognition.

Current light projecting technologies are disadvantaged for high cost,large size, and low integration, which pose as bottlenecks for thedevelopment of device functionalities built upon the light projection.Therefore, improvements over the existing light projecting technologiesare desirable for both the consumer market and the industry.

SUMMARY

Various embodiments of the present disclosure include light projectingstructures (e.g., waveguides), devices, and systems. According to oneaspect, an exemplary waveguide comprises a first surface and a secondsurface. The second surface comprises a first plurality of gratingstructures. The waveguide is configured to guide an in-coupled lightbeam to undergo total internal reflection between the first surface andthe second surface. The grating structures are configured to disrupt thetotal internal reflection to cause at least a portion of the in-coupledlight beam to couple out of the waveguide from the first surface, theportion of the in-coupled light beam coupled out of the waveguideforming out-coupled light beams. The waveguide further comprises areflective layer disposed on the second surface and covering the firstgrating structures. In some embodiments, the reflective layer comprisesone or more sub-layers, each sub-layer comprising at least one of:aluminum, silver, gold, copper, titanium, chromium, nickel, germanium,indium, tin, platinum, palladium, zinc, aluminum oxide, silver oxide,gold oxide, copper oxide, titanium oxide, chromium oxide, nickel oxide,germanium oxide, indium oxide, tin oxide, platinum oxide, palladiumoxide, zinc oxide, aluminum nitride, silver nitride, gold nitride,copper nitride, titanium nitride, chromium nitride, nickel nitride,germanium nitride, indium nitride, tin nitride, platinum nitride,palladium nitride, zinc nitride, aluminum fluoride, silver fluoride,gold fluoride, copper fluoride, titanium fluoride, chromium fluoride,nickel fluoride, germanium fluoride, indium fluoride, tin fluoride,platinum fluoride, palladium fluoride, or zinc fluoride.

In some embodiments, the second surface is parallel to the firstsurface; and the out-coupled light beams form an array of dots on aplane parallel to the first surface. In one example, the out-coupledlight beams converge from the first surface to form an upright cone oflight and then diverge to form an inverted cone of light above theupright cone of light; and a cross-section of the upright or invertedcone parallel to the first surface comprises the array of dotscorresponding to the out-coupled light beams. In another example, theout-coupled light beams diverge from the first surface to form aninverted cone of light; and a cross-section of the inverted coneparallel to the first surface comprises the array of dots correspondingto the out-coupled light beams.

In some embodiments, a cross-section of the out-coupled light beamsparallel to the first surface comprises an array of dots correspondingto the out-coupled light beams.

In some embodiments, the second surface is in an x-y plane, thein-coupled light beam propagates inside the waveguide substantiallyalong the x-direction of the x-y plane, the out-coupled light beamspropagate substantially along a z-direction normal to the x-y plane, andthe first grating structures are distributed in the x-y plane withrespect to corresponding (x, y) positions. The first grating structureis each associated with a grating depth, a duty cycle, a period, and anorientation in the x-y plane with respect to the z-direction. The firstgrating structures at different x-direction positions have at least oneof different grating depths or different grating duty cycles. The firstgrating structures at different x-direction positions have differentperiods. The first grating structures at different y-direction positionshave different orientations.

In some embodiments, the waveguide is a planar waveguide, the firstsurface and the second surface are parallel to each other and are thelargest surfaces of the waveguide, and the out-coupled light beamscouple out of the waveguide from the first surface.

In some embodiments, the waveguide further comprises an elongated thirdsurface. A light source couples light into the waveguide via the thirdsurface to form the in-coupled light beam. The light from the lightsource is collimated into a line shape corresponding to the elongatedthird surface.

In some embodiments, a prism is disposed on at least one of the firstsurface or the second surface, and a light source couples light into thewaveguide via the prism to form the in-coupled light beam.

In some embodiments, the waveguide further comprises a second pluralityof grating structures on at least one of the first surface or the secondsurface. A light source couples light into the waveguide via the secondplurality of grating structures to form the in-coupled light beam.

In some embodiments, a remainder of the in-coupled light beam undergoingthe total internal reflection reaches the fourth surface after theout-coupling at each of the grating structures. The waveguide furthercomprises a fourth surface including a first light-absorbing materiallayer for absorbing the remainder of the in-coupled light beam. Thewaveguide further comprises a second light-absorbing material layerparallel to the second surface and separated by a gap from the secondsurface.

According to another aspect, a light projecting system comprises: awaveguide comprising a first surface and a second surface, the secondsurface comprising a first plurality of grating structures; and a lightsource coupling light into the waveguide to form an in-coupled lightbeam. The waveguide is configured to guide the in-coupled light beam toundergo total internal reflection between the first surface and thesecond surface. The grating structures are configured to disrupt thetotal internal reflection to cause at least a portion of the in-coupledlight beam to couple out of the waveguide from the first surface, theportion of the in-coupled light beam coupled out of the waveguideforming out-coupled light beams. The waveguide further comprises areflective layer disposed on the second surface and covering the firstgrating structures.

In some embodiments, the light projecting system further comprises adetector configured to receive reflections of the out-coupled beams offmultiple locations on a distant object to determine distances of themultiple locations relative to the light projecting system.

According to another aspect, a light projecting system comprises: awaveguide comprising a first surface and a second surface, and one ormore lenses disposed above the first surface. The second surfacecomprises a first plurality of grating structures. The waveguide isconfigured to guide an in-coupled light beam to undergo total internalreflection between the first surface and the second surface. The gratingstructures are configured to disrupt the total internal reflection tocause at least a portion of the in-coupled light beam to couple out ofthe waveguide from the first surface, the portion of the in-coupledlight beam coupled out of the waveguide forming out-coupled light beams.The waveguide further comprises a reflective layer disposed on thesecond surface and covering the first grating structures. The one ormore lenses are configured to receive and collimate the out-coupledbeams and project the out-coupled beams into an environment.

These and other features of the systems, methods, and non-transitorycomputer readable media disclosed herein, as well as the methods ofoperation and functions of the related elements of structure and thecombination of parts and economies of manufacture, will become moreapparent upon consideration of the following description and theappended claims with reference to the accompanying drawings, all ofwhich form a part of this specification, wherein like reference numeralsdesignate corresponding parts in the various figures. It is to beexpressly understood, however, that the drawings are for purposes ofillustration and description only and are not intended as a definitionof the limits of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain features of various embodiments of the present technology areset forth with particularity in the appended claims. A betterunderstanding of the features and advantages of the technology will beobtained by reference to the following detailed description that setsforth illustrative embodiments, in which the principles of the inventionare utilized, and the accompanying drawings of which:

FIG. 1 is a graphical illustration of a light projecting system, inaccordance with various embodiments of the present disclosure.

FIG. 2 is a side-view graphical illustration of an exemplary lightprojecting system for projecting light, in accordance with variousembodiments of the present disclosure.

FIG. 3 is a side-view graphical illustration of an exemplary lightprojecting device, in accordance with various embodiments of the presentdisclosure.

FIG. 4A-FIG. 4I are side-view graphical illustrations of in-couplingfrom a light source to a light projecting structure, in accordance withvarious embodiments of the present disclosure.

FIG. 5A-FIG. 5F are side-view graphical illustrations of out-couplingfrom a light projecting structure, in accordance with variousembodiments of the present disclosure.

FIG. 6A is a side-view graphical illustration of an exemplary lightprojecting device for projecting light, in accordance with variousembodiments of the present disclosure.

FIG. 6B is a graphical illustration of grating coupling efficiency withrespect to grating depth and duty cycle, in accordance with variousembodiments of the present disclosure.

FIG. 6C is a graphical illustration of the grating coupling efficiencywith respect to the grating duty cycle, in accordance with variousembodiments of the present disclosure.

FIG. 7A is a perspective-view graphical illustration of a lightprojecting device for projecting light, in accordance with variousembodiments of the present disclosure.

FIG. 7B is a graphical illustration of a dot array corresponding to theout-coupled light beams, in accordance with various embodiments of thepresent disclosure.

FIG. 8A is a perspective-view graphical illustration of a lightprojecting device for projecting light, in accordance with variousembodiments of the present disclosure.

FIG. 8B is a graphical illustration of the out-coupled light beam anglewith respect to the grating period, in accordance with variousembodiments of the present disclosure.

FIG. 9A is a top-view graphical illustration of exemplary gratings onthe first surface, in accordance with various embodiments of the presentdisclosure.

FIG. 9B is a graphical illustration of the out-coupled light beam anglewith respect to the grating rotation angle, in accordance with variousembodiments of the present disclosure.

FIG. 10 is a top-view graphical illustration of exemplary gratings onthe first surface, in accordance with various embodiments of the presentdisclosure.

FIG. 11 is a top-view graphical illustration of exemplary gratings onthe first surface, in accordance with various embodiments of the presentdisclosure.

FIG. 12 is a graphical illustration of an exemplary light projectingsystem for projecting light, in accordance with various embodiments ofthe present disclosure.

FIG. 13 is a graphical illustration of an exemplary light projectingsystem for projecting light, in accordance with various embodiments ofthe present disclosure.

FIG. 14 is a graphical illustration of an exemplary light projectingsystem for projecting light, in accordance with various embodiments ofthe present disclosure.

DETAILED DESCRIPTION

Light projection is a key step for various applications such as 3Dfeature detection and 3D mapping. For example, depth camera modules usedfor industrial parts inspection and medical examination requiredetermining depth information. Referring to FIG. 1, in suchapplications, one or more light sources (e.g., a component of a lightprojecting system 102) may project structured light beams of apredetermined pattern onto an object (e.g., object 104 such as a face),and reflections of the light beams are captured by a detector (e.g., adetector 103) to measure various optical parameters. The lightprojecting system 102 and the detector 103 may be disposed on the samedevice (e.g., a device 101) or different devices. Though shown asseparate components, the detector 103 may be a part of the lightprojecting system 102 and configured to receive reflections of theprojected light beams off multiple locations on the distant object 104to determine distances of the multiple locations relative to the lightprojecting system 102. The light projecting system 102 may beimplemented on various systems or devices, such as mobile phones,computers, pads, wearable devices, vehicles, etc. A perfectly flatreflective plane at the position of the object may be used as areference, and reflections of the projected light off the reference canbe predetermined as reference reflection beams. The facial features canbe determined based on the differences between the detected reflectionbeams and the reference reflection beams, manifested as shifts ordistortions of the reference reflection beams. Such determination methodmay be known as the triangulation method.

Current light projection technologies for projecting the structuredlight beams employ a projection of a random dot array. The random dotarray is achieved by randomly arranging a plurality of lasers, whichinevitably drives up the cost and module size and increases integrationdifficulty.

To at least mitigate the disadvantages of the current technologies,light projecting systems and methods are disclosed. In variousembodiments, a light source may couple a light beam into a waveguide viaa surface of the waveguide, which then projects multiple beams viagratings on another surface to form distributed output beams. The lightsource can be a single laser (e.g., an edge-emitting laser, avertical-cavity surface-emitting laser (VCSEL)), a light-emitting diode,or the like, therefore obviating the need for multiple laser as requiredin existing technologies. The manufacturing cost can be further lowered,because the waveguide can be fabricated by standard lithographytechnologies. Moreover, the overall size of the light projecting systemcan be reduced due to the availability of integrating the waveguide on asubstrate. Further, the disclosed waveguide is benefited from theabsence of zeroth order diffraction interference, because zeroth ordertransmission is prohibited by the total internal reflection constraint.

As understood by people of ordinary skill in the art, a waveguide is astructure that guides waves (e.g., electromagnetic waves (light) as inthis disclosure) with minimal loss of energy by restricting expansion toone or more dimensions.

To that end, in some embodiments, a light projecting system comprises: awaveguide comprising a first surface and a second surface, the secondsurface comprising a first plurality of grating structures, a lightsource coupling light into the waveguide to form an in-coupled lightbeam, and a detector. The waveguide is configured to guide thein-coupled light beam to undergo total internal reflection between thefirst surface and the second surface. The grating structures (e.g., eachof the first grating structures) are configured to disrupt the totalinternal reflection to cause at least a portion of the in-coupled lightbeam to couple out of the waveguide from the first surface, the portionof the in-coupled light beam coupled out of the waveguide formingout-coupled light beams. The detector is configured to receivereflections of the out-coupled beams off multiple locations on a distantobject to determine distances of the multiple locations relative to thelight projecting system. Thus, the topology of the object's surface canbe determined. A light projecting device comprising the light source andthe light projecting structure (e.g., waveguide) is described in moredetails below with reference to FIG. 2 and FIG. 3. The light projectingsystem may further comprise a projection lens structure also describedin FIG. 2. The out-coupled light passes through the projection lensstructure to reach the distant object.

FIG. 2 is a side-view graphical illustration of an exemplary lightprojecting system 102 for projecting light, in accordance with variousembodiments of the present disclosure. The light projecting system 102may be implemented on various systems or devices, such as mobile phones,computers, pads, wearable devices, vehicles, etc.

As shown in FIG. 2, the exemplary light projecting system 102 maycomprise a light projecting device 211 and an optional projection lensstructure 231 (or referred to as projector lens). In some embodiments,the light projecting device 211 may comprise a light source 201 and alight projecting structure 202. The light source 201 may comprise asingle laser (e.g., an edge-emitting laser, a vertical-cavitysurface-emitting laser (VCSEL)), a light-emitting diode (LED) with lightcollimation, or the like. Alternatively, the light source 201 maycomprise multiple lasers or diodes (e.g., an edge-emitting laser array,a VCSEL array, a LED array). The light projecting structure 202 maycomprise a waveguide described in more details below. The out-coupledlight from the light projecting structure 202 can be surface normal,focusing, or defocusing.

In some embodiments, light beams emerging from the light projectingdevice 211 (out-coupled beams) may couple out from a surface of thelight projecting device 211. Then, optionally, the light beams may passthrough the projection lens structure 231 to be projected into thespace. That is the projection lens structure 231 (e.g., one or morelenses) may be disposed above the waveguide (e.g., above a first surfaceof the waveguide described later). The projection lens structure 231 maybe configured to receive the out-coupled beams and project theout-coupled beams into an environment containing the distant object.Alternatively, the light beams may be directly projected from the lightprojecting device 211 into the space. The projection lens structure 231may comprise various lens or lens combinations (e.g., one to six piecesof separate lenses) for controlling directions of the projected beams.

In some embodiments, the projection lens structure 231 may be configuredto increase or decrease the field of view of the projected beam array.For example, the projection lens structure 231 may increase the field ofview by diverging the projected beam array, or decrease the field ofview by converging the projected beam array.

In some embodiments, the projection lens structure 231 may be configuredto collimate the each out-coupled beam. For example, per workingdistance requirement of different applications, the laser waist of theprojected beam array as collimated by the projection lens structure 231can vary from 10 mm to 1 meter. Thus, the projection lens structure 231may collimate the output light to form clear image (e.g., a dot array)at a distance of interest (e.g., in the range of 10 cm to 10 m dependingon the application).

FIG. 3 is a side-view graphical illustration of an exemplary lightprojecting device 211 for projecting light, in accordance with variousembodiments of the present disclosure. The structure and operationsshown in FIG. 3 and presented below are intended to be illustrative.

In some embodiments, the light source 201 emits light to opticallycouple into the light projecting structure 202 at an in-coupling(coupling light into the light projecting structure 202) area of onesurface. The in-coupling setup can comprise end coupling, gratingcoupling, prism coupling, or the like. After entering the lightprojecting structure 202, the light undergoes total internal reflectionwithin the light projecting structure 202 between a first surface and asecond surface. The light projecting structure 202 may be made of a highrefractive index material (e.g., plexiglass, quartz glass, singlecrystal silicon, fused silica, etc.). In one example, if quartz glasswith a refractive index of 1.45 is used, the critical angle for totalinternal refraction is 44 degrees. Total internal reflection issustained when the light traveling within the light projecting structure202 strikes the first or second surface of the light projectingstructure 202 at an angle larger than the critical angle with respect tothe normal to the surface. The light travelling in the light projectingstructure 202 may couple out of the light projecting structure 202 atvarious out-coupling areas (e.g., on the first surface). For example,the out-coupling areas may be areas having out-coupling structures(e.g., a transmissive grating, a reflective grating, a reflector, etc.).

In some embodiments, the light projecting structure 202 comprises afirst surface and a second surface. At least one of the first surface orthe second surface comprises a first plurality of grating structures. Inthis disclosure, the grating structure may refer to a grating (e.g.,optical grating), which is a regularly spaced collection of identical,parallel, and elongated elements. In this figure, for example, a profileof a ridge grating is shown, and each ridge grating may compriseidentical, parallel, and elongated ridges (see Grating A in FIG. 7A).The light projecting structure guides an in-coupled light beam toundergo total internal reflection between the first surface and thesecond surface. Each of the first grating structures disrupts the totalinternal reflection to cause at least a portion of the in-coupled lightbeam to couple out of the light projecting structure, the portion of thein-coupled light beam coupled out of the light projecting structureforming out-coupled light beams. Thus, one in-coupled beam travellinginside the waveguide may couple out the waveguide through the gratingsto obtain multiple out-coupled light beams. The various in-coupling andout-coupling mechanisms are described in more details below.

FIG. 4A-FIG. 4I are side-view graphical illustrations of in-couplingfrom a light source to a light projecting structure (e.g., a planarwaveguide), in accordance with various embodiments of the presentdisclosure. The structure and operations shown in FIG. 4A-FIG. 4I andpresented below are intended to be illustrative. Assuming, the planarwaveguide is in a horizontal position, in FIG. 4A, FIG. 4F, FIG. 4G,FIG. 4H, and FIG. 4I, the light source 201 may emit light substantiallywithin a horizontal plane, while the out-coupling light propagatessubstantially within a vertical plane. In FIG. 4B, FIG. 4C, FIG. 4D, andFIG. 4E, the light source 201 may emit light substantially within avertical plane, while the out-coupling light propagates substantiallywithin the vertical plane. The horizontal and vertical planes arerelative to each other and do not constitute limitations relative to theenvironment.

In some embodiments, as shown in FIG. 4A, light emitted from the lightsource 201 may couple into the light projecting structure 202 by “endcoupling” via a surface of the light projecting structure 202. Therefractive index of the environment of the in-coupling light, therefractive index of the light projecting structure 202, the wavelength,and the incident angle of the in-coupling light on the third surface ofthe light projecting structure 202 may comply with “end coupling”conditions as understood by people skilled in the art. Inside the lightprojecting structure 202, the light undergoes total internal reflectionbetween the first and second surfaces of the light projecting structure202, and out-couples from the first surface of the light projectingstructure 202. Alternatively, if the light source 201 is large comparedto the third surface, a lens may be used to focus the light from thelight source 201 into the light projecting structure 202 by “endcoupling.”

In some embodiments, as shown in FIG. 4B and FIG. 4C, light emitted fromthe light source 201 may couple into the light projecting structure 202by “grating coupling” via an in-coupling grating. That is, the lightprojecting structure may further comprise a second plurality of gratingstructures on at least one of the first surface or the second surface. Alight source couples light into the light projecting structure via thesecond plurality of grating structures to form the in-coupled lightbeam. In FIG. 4B, the in-coupling grating may be fabricated on the firstsurface of the light projecting structure 202. Though the in-couplinggrating is shown to be level with the first surface, it may bealternatively elevated or depressed from the first surface, as long asmaintaining the subsequent total internal reflection. The refractiveindex of the environment of the in-coupling light, the refractive indexof the light projecting structure 202, the geometry of the in-couplinggrating, the wavelength, and the incident angle of the in-coupling lighton the third surface of the light projecting structure 202 comply with“grating coupling” conditions as understood by people skilled in theart. Inside the light projecting structure 202, the light undergoestotal internal reflection between the first and second surfaces of thelight projecting structure 202, and out-couples from the first surfaceof the light projecting structure 202. FIG. 4C is similar to FIG. 4Bexcept that the in-coupling grating may be fabricated on the secondsurface of the light projecting structure 202.

In some embodiments, as shown in FIG. 4D to FIG. 4I, light emitted fromthe light source 201 may couple into the light projecting structure 202by “prism coupling” via a prism. That is, the light projecting structuremay further comprise a prism disposed on at least one of: the firstsurface, the second surface, or the third surface. A light sourcecouples light into the light projecting structure via the prism to formthe in-coupled light beam. In this disclosure, “being disposed on” anobject also includes “being disposed close to” the object. Any gapbetween the prism and the light projecting structure 202 may be filledwith an optical glue or another refractive index matching material.

In FIG. 4D, the prism may be disposed on the third surface of the lightprojecting structure 202. The light source 201 may be disposed at theside the second surface and emit light into the prism. The lightundergoes one reflection within the prism and couples from the prisminto the light projecting structure 202 at the third surface. Therefractive index of the prism, the refractive index of the lightprojecting structure 202, the geometry of the prism, and the incidentangle of the light from the light source 201 comply with “gratingcoupling” conditions as understood by people skilled in the art. Insidethe light projecting structure 202, the light undergoes total internalreflection between the first and second surfaces of the light projectingstructure 202, and out-couples from the first surface of the lightprojecting structure 202. FIG. 4E is similar to FIG. 4D except that theprism may be inverted, so that the light source 201 is disposed at theside the first surface.

In FIG. 4F, the prism may be disposed on the first surface of the lightprojecting structure 202. The light source 201 may emit light thatenters the prism. At the first surface between the prism and the lightprojecting structure 202, evanescent mode of the light may couple intothe light projecting structure 202. The refractive index of the prism,the refractive index of the light projecting structure 202, the geometryof the prism, and the incident angle of the light from the light source201 comply with “phase matching” conditions as understood by peopleskilled in the art. Inside the light projecting structure 202, the lightundergoes total internal reflection between the first and secondsurfaces of the light projecting structure 202, and out-couples from thefirst surface of the light projecting structure 202. FIG. 4G is similarto FIG. 4D except that the prism may be disposed on the second surfaceof the light projecting structure 202.

In some embodiments, FIG. 4H is similar to FIG. 4D where the lightundergoes one reflection at the slope surface within the prism beforecoupling into the light projecting structure 202, except that the prismis disposed on the first surface. FIG. 4I is similar to FIG. 4H, exceptthat the prism is disposed on the second surface. The prism used in FIG.4F and FIG. 4G may be a regular prism, and the prism used in FIG. 4H andFIG. 4I may be a wedge prism.

FIG. 5A-FIG. 5F are side-view graphical illustrations of out-couplingfrom a light projecting structure (e.g., a planar waveguide), inaccordance with various embodiments of the present disclosure. Thestructure and operations shown in FIG. 5A-FIG. 5F and presented beloware intended to be illustrative. For simplicity, in-coupling and lighttraveling inside the light projecting structure 202 are omitted in FIG.5A-FIG. 5F.

In some embodiments, the light projecting structure comprises a planarwaveguide. The first surface and the second surface are parallel to eachother and are the largest surfaces of the planar waveguide. Theout-coupled light beams couple out of the light projecting structurefrom the first surface. The first surface or the second surfacecomprises the first plurality of grating structures. When the secondsurface comprises the first plurality of grating structures, the lightprojecting structure may further comprise a metal layer disposed on thesecond surface. Alternatively, the first grating structures comprisevolumetric gratings between the first surface and the second surface.That is, the in-coupled light inside the light projecting structure 202undergoes total internal reflection. While the rest continues totalinternal reflection, a portion of the light may break free of the totalinternal reflection when striking an out-coupling structure on the firstsurface, on the second surface, or inside the waveguide, andsubsequently exit the waveguide from one of its surfaces (e.g., thefirst surface). Various out-coupling structures (transmissive grating,reflective grating, reflector, etc.) are described below.

In FIG. 5A-FIG. 5C, the illustrated waveguide structure includinggratings may allow one or multiple diffraction orders to couple out ofthe waveguide. In some embodiments, as shown in FIG. 5A, gratings may befabricated at various out-coupling areas on the first surface of thelight projecting structure 202. The out-coupling areas may correspond toareas of total internal reflection, and a portion of the light travelinginside the waveguide may couple out of the waveguide from each of theout-coupling areas (e.g., into the air).

In some embodiments, as shown in FIG. 5B (configuration 1), diffractiongratings may be fabricated at various out-coupling areas on the secondsurface of the light projecting structure 202. That is, that waveguidemay comprise: (1) a bottom layer with gratings fabricated on top, thebottom layer having a first refractive index, and (2) a top layer with acomplementary shape with the bottom layer. The out-coupling areas maycorrespond to areas of total internal reflection, and a portion of thelight striking each of the out-coupling areas may bend toward the firstsurface and subsequently couple out of the waveguide from the firstsurface.

Similarly, FIG. 5B also illustrates a configuration 2 with gratingsfabricated on the second surface. The gratings may have the samerefractive index as the waveguide or have a different refractive index.

In some embodiments, as shown in FIG. 5C, a micro lens array may bedisposed on the first surface corresponding to the positions of theout-coupling areas in FIG. 5B, such that the out-coupling light can becollimated, made parallel, or otherwise controlled.

In some embodiments, as shown in FIG. 5D, refractive gratings may befabricated at various out-coupling areas on the first surface of thelight projecting structure 202. For example, gratings of a triangleprofile as shown may be etched away from the first surface. The gratingscorrespond to the out-coupling areas, from which a portion of the totalinternal reflection light may couple out of the waveguide.

In some embodiments, as shown in FIG. 5E, reflective gratings may befabricated at various out-coupling areas on the second surface of thelight projecting structure 202. For example, gratings of a triangleprofile as shown may be etched away from the second surface. Thegratings correspond to the out-coupling areas, from which a portion ofthe total internal reflection light may be reflected towards the firstsurface and subsequently couple out of the waveguide.

In some embodiments, as shown in FIG. 5F, volumetric gratings may befabricated within the waveguide. For example, the periodicity of thevolumetric gratings is in alternating refractive index between repeatingperiodic sections. The refractive index changing interfaces maycorrespond to the out-coupling areas, from which a portion of the totalinternal reflection light may be reflected towards the first surface andsubsequently couple out of the waveguide.

Various configurations of the first grating structures may control theout-coupled light beams. As described below, the out-coupling efficiencymay be determined by the grating depth (also referred to as “thickness”)and grating duty cycle (FIG. 6A-FIG. 6C), the angle of the out-coupledlight beam with respect to surface normal may be determined by thegrating period (FIG. 8A-FIG. 8B), and the rotation angle of theout-coupled light beam may be determined with the grating orientation(FIG. 9A-FIG. 9B).

In some embodiments, the gratings (first grating structures) disrupt thetotal internal reflection to cause the out-coupled light beams toproject from the first surface, the out-coupled light beams forming anarray of dots on a plane parallel to the first surface. In one example,the out-coupled light beams propagates normal to the first surface, anda cross-section of the out-coupled light beams parallel to the firstsurface comprises a random array of dots corresponding to theout-coupled light beams. In another example, the out-coupled light beamsform an inverted cone of light, and a cross-section of the inverted coneparallel to the first surface comprises a random array of dotscorresponding to the out-coupled light beams (FIG. 7B). As describedbelow, the dot pattern is not limited to the illustrated examples, andmay comprise various other configurations. The descriptions below withreference to FIG. 6A to FIG. 9B may borrow the coordinate system shownin FIG. 10 or FIG. 11. That is, the first surface (or the secondsurface) of the waveguide is in an x-y plane comprising an x-directionand a y-direction perpendicular to each other, the in-coupled light beampropagates inside the light projecting structure substantially along thex-direction of the x-y plane, and the out-coupled light beams propagatesubstantially along a z-direction normal to the x-y plane. The gratingstructures may be randomly distributed in the x-y plane with respect tocorresponding (x, y) positions. In some embodiments, the dimension ofthe grating is about 2 μm to 30 μm, the number of gratings on thewaveguide is about couple hundreds to one million, and the average pitch(separation between closest gratings) is about 5 μm to 100 μm.

FIG. 6A is a side-view graphical illustration of an exemplary lightprojecting device 211 for projecting light, in accordance with variousembodiments of the present disclosure. The structure and operationsshown in FIG. 6A and presented below are intended to be illustrative.FIG. 6A may correspond to FIG. 5A described above, and the gratingout-coupling mechanism is described below.

In some embodiments, the direction of the out-coupled light beam mayfollow the following formula:

$\begin{matrix}{{\sin\;\theta_{m}} = {\frac{m\;\lambda}{\Gamma} - {n \times \sin\;\theta_{i}}}} & (1)\end{matrix}$

where m is the diffraction order, λ is the wavelength, Γ is the periodof the grating, n is the refractive index of the waveguide, θ_(m) is theangle of the out-coupling beam with respect to the normal of the firstsurface, and θ_(i) is the angle of the beam undergoing total internalreflection inside the waveguide with respect to the normal of the firstsurface.

In some embodiments, the described out-coupling (light undergoing totalinternal reflection inside a waveguide couples out of the waveguide fromareas having grating structures) occurs when the effective index of the+1 diffractive order (m=1) matches the effective index of the modesupported by the waveguide. Thus, to obtain out-coupling beamspropagating parallel to the normal, and therefore (that is, θ_(m)=0),the grating period (labeled as “period” in the figure) can be obtainedas:

$\begin{matrix}{\Gamma = \frac{\lambda}{n \times \sin\;\theta_{i}}} & (2)\end{matrix}$

For example, when the waveguide is quartz glass (n=1.45), λ=940 nm, andθ_(i)=60°, Γ can be obtained to be 748 nm. Accordingly, the gratingperiod can affect the angle of the out-coupling beam with respect to thenormal.

Substituting equation (2) into equation (1), it can be obtained that:sin θ_(m)=(m−1)×n×sin θ_(i)  (3)

Further, based on the condition for total internal reflection with acritical angle θ_(c):

$\begin{matrix}{{\theta_{i} > \theta_{c}} = {\arcsin( \frac{1}{n} )}} & (4)\end{matrix}$

It can be obtained that

${{\sin\;\theta_{i}} > \frac{1}{n}},$and therefore:n×sin θ_(i)>1  (5)

To satisfy both (3) and (5) with m being an integer and |sin θ_(m)|≤1, mcan only be 1. Therefore, the described out-coupling (light undergoingtotal internal reflection inside a waveguide coupling out of thewaveguide from areas having the grating structures) may yield only them=+1 order of out-coupled light, without interference of light of othertransmissive diffraction orders. This is one of the advantages absent inexisting light projecting technologies.

FIG. 6B is a graphical illustration of simulated coupling efficiencywith respect to grating depth and duty cycle, in accordance with variousembodiments of the present disclosure.

In some embodiments, the grating has a geometry for a high couplingefficiency, that is, the percentage (portion) of the light undergoingtotal internal reflection that couples out of the waveguide at thegrating. Thus, in this context, the coupling efficiency can beunderstood as an out-coupling efficiency. When the grating period isfixed, the coupling efficiency is determined by the grating depth andduty cycle (percentage of each period that the ridge structureoccupies). Referring to the labels “ridge width” and “period” in FIG. 6Aand FIG. 9A, the duty cycle may be obtained as dividing the ridge widthby the period. The duty cycle may be alternatively be referred to as afilling factor. For FIG. 6B, when λ=940 nm, and θ_(i)=60°, Γ can beobtained to be 748 nm.

FIG. 6B shows simulated coupling efficiencies for two differentwaveguide modes (that is, TE mode and TM mode light traveling in thewaveguide). The x-axis represents the duty cycle, and the y-axisrepresents the grating depth. Higher coupling efficiencies arerepresented by brighter areas. For the TE mode, the highest couplingefficiency is 9.8%, occurring at duty cycle of 0.43 and a thickness of0.35 μm. For the TM mode, the highest coupling efficiency is 2.8%,occurring at duty cycle of 0.52 and a thickness of 0.3 μm. Therefore,the grating depth and duty cycle can be designed to achieve variouscoupling efficiencies. Further, by tuning the grating depth, a couplingefficiency higher than the illustrated 9.8% efficiency can be achieved.

In one example, extracting from the TE mode diagram in FIG. 6B, whenλ=940 nm, θ_(i)=60°, Γ=748 nm, and thickness=0.35 μm, the couplingefficiency with respect to the duty cycle can be obtained as shown inFIG. 6C. The same peak coupling efficiency is at 9.8%, with a duty cycleof 0.43 and a thickness of 0.35 μm.

In some embodiments, as a portion of the light undergoing total internalreflection in the waveguide couples out of the waveguide at eachgrating, the power of the light remaining in the waveguide decreasesafter each out-coupling event. To ensure that out-coupled light beams inthe dot array have about similar powers, the gratings can be designedsuch that the coupling efficiency increases as the distance of thegrating from the light source 201 increases. For example, referring backto FIG. 6A, grating Y can have a larger coupling efficiency than that ofgrating X, by tuning the duty cycle and grating depth, to ensure thatthe out-coupled light from grating Y and grating X have similar powers.

Thus, in some embodiments, each of the grating structures is associatedwith an out-coupling efficiency. The out-coupling efficiency increasesmonotonically along the x-direction. The out-coupling efficiency dependson a grating depth and a duty cycle of the grating structure. At leastone of a grating depth or a duty cycle of the grating period varies inthe x-direction to cause the out-coupling efficiency to increasemonotonically along the x-direction. In one example, a grating depth ofthe grating structure increases monotonically in the x-direction,causing the out-coupling efficiency to increase monotonically along thex-direction. In another example, a duty cycle of the grating structureincreases monotonically in the x-direction causing the out-couplingefficiency to increase monotonically along the x-direction. In anotherexample, the x-y plane comprises a plurality of regions corresponding tovarious ranges of positions along the x-direction, the regionscomprising a first region and a second region. The first region is theclosest to an area of the in-coupled light beam coupling into the lightprojecting structure. The second region is the furthest from the area ofthe in-coupled light beam coupling into the light projecting structure.The grating structures in the same region have similar out-couplingefficiencies. The monotonic increase of the out-coupling efficiencyalong the x-direction causes a power of the out-coupled light beam fromeach of the grating structures in the first region to be similar to apower of the out-coupled light beam from each of the grating structuresin the second region.

FIG. 7A is a perspective-view graphical illustration of a lightprojecting device 211 for projecting light, in accordance with variousembodiments of the present disclosure. The structure and operationsshown in FIG. 7A and presented below are intended to be illustrative.

As shown in FIG. 7A, in some embodiments, the light projecting structure202 may comprise a planar waveguide with gratings fabricated on thefirst surface. The light projecting structure 202 shown in FIG. 7A maybe similar to the light projecting structure 202 shown in FIG. 6A,except that the out-coupling light beams in FIG. 7A are normal to thefirst surface. The light source 201 may comprise one or more lasers orLEDs with light collimation. The lasers or LEDs may be arranged in a rowto couple into a side surface of the planar waveguide.

In some embodiments, the gratings (e.g., grating A, grating B, gratingC, grating D, etc.) may be fabricated at random locations on the firstsurface. The gratings may have the same grating period. From eachgrating, one out-coupling light beam couples out of the waveguide.Accordingly, when viewed from top, the out-coupling light beams may forma random dot array as shown in FIG. 7B. The illustrated dot arraypattern is merely exemplary. Based on configuring the grating structures(e.g., by tuning period, orientation, depth, duty cycle, (x, y, z)positions on the waveguide, number, etc.), any dot array pattern can beachieved to satisfy the application requirements.

FIG. 8A is a perspective-view graphical illustration of a lightprojecting device 211 for projecting light, in accordance with variousembodiments of the present disclosure. The structure and operationsshown in FIG. 8A and presented below are intended to be illustrative.

The light projecting device 211 may be similar in FIG. 7A and FIG. 8A,also providing a random dot array, except that the gratings in FIG. 8Amay have different grating periods. As shown in FIG. 8A, in someembodiments, the gratings (e.g., grating E, grating F, grating G,grating H, etc.) may have different grating periods Γ. According toequation (1) described above, θ_(m) changes with the grating period Γ.That is, the out-coupling light beam may propagate at various angleswith respect to the normal direction. Thus, the change in θ_(m) may alsoincrease the randomness of the dot array. A plot of the out-coupledlight beam angle (in the x-z plane with respect to the z-direction)against the grating period is shown in FIG. 8B. As shown, within thesame vertical plane normal to the first surface and along the directionof the light traveling inside the waveguide (x-direction), theout-coupled light beam can be manipulated between −5 to 15 degrees withrespect to the normal direction, by changing the grating period. Thoughthe out-coupled beam may also have a y-direction component, FIG. 8A andFIG. 8B focus on the x-direction component.

Thus, in some embodiments, the grating structures are each associatedwith a period, and the period varies for the grating structures alongthe x-direction. The variation of the period causes the out-coupledlight beams to couple out of the waveguide at a range of angulardeviations in the x-direction. In one example, the period monotonicallyvaries along the x-direction. The monotonic variation of the periodalong the x-direction causes the out-coupled light beams to couple outof the light projecting structure at a range of angular deviations inthe x-direction.

FIG. 9A is a top-view graphical illustration of exemplary gratings onthe first surface, in accordance with various embodiments of the presentdisclosure. As shown in FIG. 9A, in some embodiments, the gratings mayhave various orientations within the x-y plane. The grating orientationcan be illustrated with reference to the orientation of the ridges ofthe grating. For example, grating M may be oriented with its ridgesperpendicular to the x-direction, grating N may be oriented with itsridges at a positive rotation angle to the x-direction, and grating Kmay be oriented with its ridges at a negative rotation angle to thex-direction.

In some embodiments, the in-coupled light travels from left to rightinside the waveguide in the x-direction. The out-coupled light fromgrating M has a y-direction component of zero. That is, ignoring thex-direction component, the out-coupled light from gratin M propagates inthe z-direction. The out-coupled light from grating N of a positiverotation angle has a negative y-direction component. That is, ignoringthe x-direction component, the out-coupled light from gratin Npropagates in the z-negative-y direction. The out-coupled light fromgrating K of a negative rotation angle has a positive y-directioncomponent. That is, ignoring the x-direction component, the out-coupledlight from gratin K propagates in the z-positive-y direction. Thus,considering the out-coupled beams from the gratings M, N, and, K, theout-coupled beams converge in the y-z plane. FIG. 9A is a simplifiedillustration of the grating orientation control described below in FIG.10 for obtaining converging out-coupled beams. The reverse of FIG. 9Bfor obtaining diverging out-coupled beams is described below in FIG. 11.

A plot of the out-coupled light beam angle (in the y-z plane withrespect to the z-direction) against the grating rotation angle (withrespect to the x-direction) is shown in FIG. 9B. In this plot, theout-coupled light beam angle can be manipulated between about −70 to 70degrees with respect to the reference direction, by changing the gratingorientation between 45 and −45 degrees with respect to the x-direction.FIG. 9B is merely exemplary, and alternative direction reference systemsmay be used. Though the out-coupled beam may also have a x-directioncomponent, FIG. 9A and FIG. 9B focus on the y-direction component.

Thus, in some embodiments, the grating structures are each associatedwith a degree of rotation with respect to the z-direction, and thedegree of rotation varies for the grating structures along they-direction. The variation of the degree of rotation causes theout-coupled light beams to couple out of the waveguide at a range ofangular deviations in the y-direction. In one example, the degree ofrotation varies monotonically clockwise or counter-clockwise. Themonotonic variation of the degree of rotation causes the out-coupledlight beams to propagate at various y-direction components.

Each of FIG. 10 and FIG. 11 is a top-view graphical illustration ofexemplary gratings (first grating structures) on the first surface, inaccordance with various embodiments of the present disclosure.Alternatively, the gratings may be fabricated on the second surface oraccording to another configuration shown in FIG. 5A-FIG. 5F above. Thestructure and operations shown in FIG. 10 and FIG. 11 and presentedbelow are intended to be illustrative. The gratings in FIG. 10 and FIG.11 may have combined controlling the out-coupling efficiency by thegrating depth and duty cycle, controlling the angle of the out-coupledlight beam with respect to normal by the grating period, and controllingthe rotation angle of the out-coupled light beam by the gratingorientation described above from FIG. 6A-FIG. 9B. As shown in FIG. 10and FIG. 11, the planar waveguide is in an x-y plane, and thez-direction is the surface normal direction (which is perpendicular tothe x-y plane). In this disclosure, the x-direction and y-direction aredefined as shown in this figure. The z-direction is normal to the x-yplane and pointing out of the plane of the paper. The x, y, and zdirections may also be referred to as positive x, y, and z directions,and their opposite directions may be referred to as negative x, y, and zdirections. The in-coupled light may enter the waveguide from left,portions of which couple out of the waveguide through the gratings, withsome residue light (also referred to as remainder light) left andcontinuing in the x-direction. The in-coupled light may originate fromone or more lasers. The first grating structure is each associated witha grating depth, a duty cycle, a period, and an orientation in the x-yplane with respect to the z-direction. The first grating structures atdifferent x-direction positions have at least one of different gratingdepths or different grating duty cycles. The first grating structures atdifferent x-direction positions have different periods. The firstgrating structures at different y-direction positions have differentorientations.

In some embodiments, the waveguide further comprises an elongated thirdsurface. The position of the third surface relative to the first andsecond surfaces are described above. A light source couples light intothe waveguide via the third surface (in the “light incident direction”shown in FIG. 10 and FIG. 11) to form the in-coupled light beam. Thelight from the light source is collimated into a line shapecorresponding to the elongated third surface. In one example when asingle laser is used, the laser output beam may be collimated by acollimation lens or lens array into a line shape, which lies along thethird surface of the planar waveguide and can subsequently couple intothe planar waveguide through the third surface.

In some embodiments, the divergence of the out-coupled beams may becontrolled via the grating orientation and the grating period. Forexample, the divergence of the out-coupled beams in the y-direction maybe controlled via the grating orientation, and the divergence of theout-coupled beams in the x-direction may be controlled via the gratingperiod. In the y-direction of FIG. 10 and FIG. 11, the angle of theout-coupled beam in the y-z plane (a plane containing the y-directionaxis and the z-direction axis) with respect to the z-direction varieswith the rotational orientation of the grating. Detailed explanationscan be referred to the discussion above with reference to FIG. 9A andFIG. 9B. In the x-direction of FIG. 10 and FIG. 11, the angle of theout-coupled beam in the x-z plane (a plane containing the x-directionaxis and the z-direction axis) with respect to the z-direction varieswith the grating period. The output angle of the out-coupled beamincreases with the grating period. Detailed explanations can be referredto the discussion above with reference to FIG. 8A and FIG. 8B.Therefore, the grating orientation and the grating period may becontrolled to obtain converging out-coupled beams (e.g., in a cone shapeconverging from the first surface) or diverging out-coupled beams (e.g.,in an inverted cone shape diverging from the first surface).

FIG. 10 shows an exemplary grating orientation and period control forobtaining converging out-coupled beams, and FIG. 11 shows an exemplarygrating orientation and period control for obtaining divergingout-coupled beams.

In some embodiments, FIG. 10 and FIG. 11 illustrate exemplary gratingstructure with grating orientation control. In FIG. 10, the gratingorientation may change from bottom to top in the y-direction, such thatthe gratings appear to rotate clockwise with respect to the normal tothe first surface. That is, in FIG. 10, assuming that the y-axisdirection is the reference direction, the gratings in the middlehorizontal section of the first surface have no rotation, the gratingsin the bottom horizontal section of the first surface have negativerotations (tilting left), and the gratings in the top horizontal sectionof the first surface have positive rotations (tilting right), so thatthe out-coupled beam from the topmost grating has the most negativey-direction component, and the out-coupled beam from the bottommostgrating has the most positive y-direction component, consistent withFIG. 9B and its description. That is, the grating structures along they-direction may have orientations rotating in a clockwise direction tocause the out-coupled light beams to converge from the first surface ina y-z plane. In FIG. 11, the grating orientation may change from bottomto top in the y-direction, such that the gratings appear to rotatecounter-clockwise with respect to the normal to the first surface. Thatis, in FIG. 11, assuming that the y-axis direction is the referencedirection, the gratings in the middle horizontal section of the firstsurface have no rotation, the gratings in the bottom horizontal sectionof the first surface have positive rotations (tilting right), and thegratings in the top horizontal section of the first surface havenegative rotations (tilting left), so that the out-coupled beam from thetopmost grating has the most positive y-direction component, and theout-coupled beam from the bottommost grating has the most negativey-direction component, consistent with FIG. 9B and its description. Thatis, the grating structures along the y-direction have orientationsrotating in a counter-clockwise direction to cause the out-coupled lightbeams to diverge from the first surface in a y-z plane. Thus, changingthe grating orientation (e.g., clockwise or counter-clockwisemonotonically in the y-direction) expands the out-coupled light frombeing only in the surface normal direction (normal to the first surface)to having a certain field-of-view in the y-direction. The field of viewin the y-direction converges in FIG. 10 and diverges in FIG. 11,contributing to the convergence and divergence of the out-coupled beamsrespectively.

In some embodiments, FIG. 10 and FIG. 11 also illustrate exemplarygrating structure with grating period control. In FIG. 10, the gratingperiod decreases in the x-direction, so that the first out-coupled beamin the x-direction has the most positive x-direction component, and thelast out-coupled beam in the x-direction has the most negativex-direction component, consistent with FIG. 8B and its description.Thus, the out-coupled beams converge in the x-direction. In FIG. 11, thegrating period increases in the x-direction, so that the firstout-coupled beam (coupled out of the first grating) in the x-directionhas the most negative x-direction component, and the last out-coupledbeam (coupled out of the last grating) in the x-direction has the mostpositive x-direction component, consistent with FIG. 8B and itsdescription. Thus, changing the grating period (e.g., increasing ordecreasing monotonically in the x-direction) expands the out-coupledlight from being only in the surface normal direction (normal to thefirst surface) to having a certain field-of-view in the x-direction. Theperiod may decrease monotonically in the x-direction to cause theout-coupled light beams to converge from the first surface in an x-zplane. The period may increase monotonically in the x-direction to causethe out-coupled light beams to diverge from the first surface in an x-zplane. The field of view in the x-direction converges in FIG. 10 anddiverges in FIG. 11, contributing to the convergence and divergence ofthe out-coupled beams respectively.

Referring to FIG. 10, the grating period's decrease (e.g., monotonicdecrease) in the x-direction combined with the grating orientation'sclockwise rotation in the y-direction (e.g., monotonic clockwiserotation with respect to the z-direction for gratings in they-direction) may cause the out-coupled light beams to converge from thefirst surface. That is, the period decreases monotonically in thex-direction and the grating structures along the y-direction haveorientations rotating in a clockwise direction to cause the out-coupledlight beams to converge from the first surface. In one example, theconverged beams may form an upright cone projected out from the firstsurface and converging towards a point above the first surface, but oncepast the converging point, the beams will diverge to form an invertedcone of light on top of the upright cone.

Referring to FIG. 11, the grating period's increase (e.g., monotonicincrease) in the x-direction combined with the grating orientation'scounter-clockwise rotation in the y-direction (e.g., monotoniccounter-clockwise rotation with respect to the z-direction for gratingsin the y-direction) may cause the out-coupled light beams to divergefrom the first surface. That is, the period increases monotonically inthe x-direction and the grating structures along the y-direction haveorientations rotating in a counter-clockwise direction to cause theout-coupled light beams to diverge from the first surface. In oneexample, the diverged beams may form an inverted cone projected out fromthe first surface and diverging from the first surface.

In some embodiments, the light power in the waveguide decreases alongthe propagation direction (x-direction in FIG. 10 and FIG. 11), andhence the power of the total-internal-reflection beams impinging on thegratings for out-coupling decreases along the propagation direction. Toobtain a uniform output power for the out-coupled beams, theout-coupling efficiency may increase along the propagation direction tocompensate for the loss of power. The out-coupling efficiency mayincrease monotonically in the propagation direction. The out-couplingefficiency can be varied by changing the grating depth and/or gratingduty cycle (see discussion of FIG. 6B and FIG. 6C above). Anyout-coupling efficiency level can be achieved with an appropriatecombination of grating depth and grating duty cycle pair. The gratingthickness may or may not increase monotonically in the propagationdirection. The grating duty cycle may or may not increase monotonicallyin the propagation direction. Each of the grating thickness and thegrating duty cycle does not have to obey any monotonic trend in thepropagation direction, as long as the combinations of the gratingthickness and the grating duty result in increasing out-couplingefficiencies for the out-coupled beams along the propagation direction.

Referring to FIG. 10 and FIG. 11, in some embodiments, the first surfacecan be visualized as strips of total intern reflection regions (TIRregion 1, TIR region 2, etc.), with corresponding out-couplingefficiencies η₁, η₂, . . . η_(n) increasing from η₁ to η_(n) in order tomaintain a constant output power. In one example, the relationship maybe P_(n−1)×η_(n−1)=P_(n)×η_(n), where P_(n)=P_(n−1)×(1−η_(n−1)). Tochange the coupling efficiency η, one can change the duty cycle and/orthe grating depth.

In some embodiments, the distribution of the grating locations on thefirst surface in FIG. 10 and FIG. 11 may be random. That is,notwithstanding complying with the described trend in grating period,grating depth, grating duty cycle, and grating orientation, if the firstsurface (or the second surface) is in an x-y plane, the gratings arerandomly distributed in the x-y plane with respect to corresponding (x,y) positions. Here, the random distribution means that the gratings maynot be fixed at periodic locations (e.g., 2D lattice locations, evenlyspaced locations, etc.) on the first or the second surface. The randomdot array described herein may correspond to this random distribution ofthe grating locations. The random distribution of the grating locationscan minimize the algorithm error that is detrimental to detection basedon the out-coupled beams. The algorithm error is often caused byperiodic or other non-random pattern trends, for which the algorithm runby the detector for detecting differences between reflections fromdifferent structured light beams would have a hard time to distinguishone part of the patterns from another part as they appear to be thesame.

Although the gratings in FIG. 10 and FIG. 11 are shown as three ridges,each grating can contain any number of ridges or another alternativegrating structure (e.g., rib, buried ridge, diffused ridge, etc.). Theridge profile may be square, round, triangular, etc. Though shown assquare in FIG. 10 and FIG. 11, the outer shape of each grating mayalternatively be circular, oval, rectangular, etc. The size of gratingmay vary from 1 period (around 1 μm) to the whole pixel size (around 30μm). In some embodiments, if the grating is sufficiently large such thatthe diffraction limit can be ignored, the dot size will increase withthe grating size, and the size of the grating can be manipulated toobtain the ideal size for the dot (beam size of projected light beam).For example, if an application requires more dots, the size of thegrating can be reduced to pack more dots into a fixed area (e.g., thefirst surface). If an application requires brighter dots (highersignal-to-noise ratio), the size of the grating can be increased sincelarger dots have more power and thus are brighter.

FIG. 12 is a graphical illustration of an exemplary light projectingsystem 102 for projecting light, in accordance with various embodimentsof the present disclosure. The light projecting system 102 may implementthe in-coupling mechanism described above with reference to FIG. 4H andthe out-coupling mechanism described above with reference to FIG. 5B(configuration 2).

In some embodiments, the waveguide further comprises a reflective layerdisposed on the second surface and covering the grating structures. Thereflective layer may comprise one or more sub-layers of metal (e.g.,alloy) and/or non-metal (e.g., dielectric). In one example, thereflective layer comprises one or more sub-layers, each sub-layercomprising at least one of: aluminum, silver, gold, copper, titanium,chromium, nickel, germanium, indium, tin, platinum, palladium, zinc,aluminum oxide, silver oxide, gold oxide, copper oxide, titanium oxide,chromium oxide, nickel oxide, germanium oxide, indium oxide, tin oxide,platinum oxide, palladium oxide, zinc oxide, aluminum nitride, silvernitride, gold nitride, copper nitride, titanium nitride, chromiumnitride, nickel nitride, germanium nitride, indium nitride, tin nitride,platinum nitride, palladium nitride, zinc nitride, aluminum fluoride,silver fluoride, gold fluoride, copper fluoride, titanium fluoride,chromium fluoride, nickel fluoride, germanium fluoride, indium fluoride,tin fluoride, platinum fluoride, palladium fluoride, or zinc fluoride.When the grating are fabricated on the second surface (as shown) or onthe first surface, some amount of optical power may leak out of thewaveguide (e.g., downward) due to symmetric first order diffraction. Tominimize or suppress such leakage and maximize the coupling efficiency,a reflective layer (e.g., metal layer or a high reflection coatinglayer) may be deposited on the second surface. The metal can bealuminum, silver, gold, copper, or another high reflection metal.

FIG. 13 is a graphical illustration of an exemplary light projectingsystem 102 for projecting light, in accordance with various embodimentsof the present disclosure. The light projecting system 102 may implementthe in-coupling mechanism described above with reference to FIG. 4H andthe out-coupling mechanism described above with reference to FIG. 3.

In some embodiments, light-absorbing material layers as shown can beused to minimize the background noise caused by leakage light fromhigher grating modes or by residue light from incomplete coupling. Tominimize emitting the residue light from the waveguide, alight-absorbing material layer may be disposed on the sidewall of thewaveguide directly (at the end of the light propagation in thewaveguide). To reduce the leakage light from other grating modes, alight-absorbing material layer may be disposed with a gap from thesecond surface, to prevent from breaking the total internal reflectioncondition. The light-absorbing material layer can be a (colored)anodized aluminum layer, a rough surface, a black carbon paint layer, oranother light-absorbing material layer.

That is, the light projecting structure may further comprise a fourthsurface, a first light-absorbing material layer, and a secondlight-absorbing material layer. A remainder of the in-coupled light beamundergoing the total internal reflection reaches the fourth surfaceafter the out-coupling at each of the grating structures. The fourthsurface comprises the light-absorbing material layer for absorbing theremainder of the in-coupled light beam. The second light-absorbingmaterial layer is parallel to the second surface and is separated by agap from the second surface. The second light-absorbing material layermay absorb light that leaks out of the waveguide from the secondsurface. The gap may prevent absorbing in-coupled light still travellinginside the waveguide.

FIG. 14 is a graphical illustration of an exemplary light projectingsystem 102 for projecting light, in accordance with various embodimentsof the present disclosure. The light projecting system 102 may implementthe in-coupling mechanism described above with reference to FIG. 4H andthe out-coupling mechanism described above with reference to FIG. 3.

In some embodiments, as shown, a residue light out-coupling setup may beadded to couple the residue light out of the waveguide (at the end ofthe light propagation in the waveguide), for example, via end coupling,grating coupling, or prism coupling described above. A detector such asa monitoring photo diode (e.g., silicon, germanium, or another diode)may be used to detect the out-coupled residue light. In one example, ifany accident (e.g., chip cracking, water damage, vapor damage, laserdislocation, in-coupling prism dislocation, or another failure event)happens, the total internal reflection condition will be broken at thefailing spot (an example of which is shown and labeled in the figure),which will result in change of the residue light. With a thresholdingalgorithm, the event of residue light changing can be timely detected bythe monitoring photo diode, and the input laser can be shut offaccordingly to ensure eye safety. If the input laser is not shut off,some of the laser beams may escape from the light projecting system withan uncontrolled power that may cause eye damage.

The various features and processes described above may be usedindependently of one another, or may be combined in various ways. Allpossible combinations and sub-combinations are intended to fall withinthe scope of this disclosure. In addition, certain method or processblocks may be omitted in some implementations. The methods and processesdescribed herein are also not limited to any particular sequence, andthe blocks or states relating thereto can be performed in othersequences that are appropriate. For example, described blocks or statesmay be performed in an order other than that specifically disclosed, ormultiple blocks or states may be combined in a single block or state.The exemplary blocks or states may be performed in serial, in parallel,or in some other manner. Blocks or states may be added to or removedfrom the disclosed exemplary embodiments. The exemplary systems andcomponents described herein may be configured differently thandescribed. For example, elements may be added to, removed from, orrearranged compared to the disclosed exemplary embodiments.

Throughout this specification, plural instances may implementcomponents, operations, or structures described as a single instance.Although individual operations of one or more methods are illustratedand described as separate operations, one or more of the individualoperations may be performed concurrently, and nothing requires that theoperations be performed in the order illustrated. Structures andfunctionality presented as separate components in exemplaryconfigurations may be implemented as a combined structure or component.Similarly, structures and functionality presented as a single componentmay be implemented as separate components. These and other variations,modifications, additions, and improvements fall within the scope of thesubject matter herein.

Although an overview of the subject matter has been described withreference to specific exemplary embodiments, various modifications andchanges may be made to these embodiments without departing from thebroader scope of embodiments of the present disclosure. Such embodimentsof the subject matter may be referred to herein, individually orcollectively, by the term “invention” merely for convenience and withoutintending to voluntarily limit the scope of this application to anysingle disclosure or concept if more than one is, in fact, disclosed.

The embodiments illustrated herein are described in sufficient detail toenable those skilled in the art to practice the teachings disclosed.Other embodiments may be used and derived therefrom, such thatstructural and logical substitutions and changes may be made withoutdeparting from the scope of this disclosure. The Detailed Description,therefore, is not to be taken in a limiting sense, and the scope ofvarious embodiments is defined only by the appended claims, along withthe full range of equivalents to which such claims are entitled.

As used herein, the term “or” may be construed in either an inclusive orexclusive sense. Moreover, plural instances may be provided forresources, operations, or structures described herein as a singleinstance. Additionally, boundaries between various resources,operations, engines, and data stores are somewhat arbitrary, andparticular operations are illustrated in a context of specificillustrative configurations. Other allocations of functionality areenvisioned and may fall within a scope of various embodiments of thepresent disclosure. In general, structures and functionality presentedas separate resources in the exemplary configurations may be implementedas a combined structure or resource. Similarly, structures andfunctionality presented as a single resource may be implemented asseparate resources. These and other variations, modifications,additions, and improvements fall within a scope of embodiments of thepresent disclosure as represented by the appended claims. Thespecification and drawings are, accordingly, to be regarded in anillustrative rather than a restrictive sense.

Conditional language, such as, among others, “can,” “could,” “might,” or“may,” unless specifically stated otherwise, or otherwise understoodwithin the context as used, is generally intended to convey that certainembodiments include, while other embodiments do not include, certainfeatures, elements and/or steps. Thus, such conditional language is notgenerally intended to imply that features, elements and/or steps are inany way required for one or more embodiments or that one or moreembodiments necessarily include logic for deciding, with or without userinput or prompting, whether these features, elements and/or steps areincluded or are to be performed in any particular embodiment.

The invention claimed is:
 1. A waveguide, comprising: a first surface,and a second surface, wherein: the waveguide is a planar waveguide; thefirst surface and the second surface are parallel to each other and arethe largest surfaces of the waveguide; the second surface comprises afirst plurality of grating structures; the waveguide is configured toguide an in-coupled light beam to undergo total internal reflectionbetween the first surface and the second surface; the grating structuresare configured to disrupt the total internal reflection to cause atleast a portion of the in-coupled light beam to couple out of thewaveguide from the first surface, the portion of the in-coupled lightbeam coupled out of the waveguide forming out-coupled light beams; andthe waveguide further comprises a reflective layer disposed on thesecond surface and covering the first grating structures.
 2. Thewaveguide of claim 1, wherein: the reflective layer comprises one ormore sub-layers, each sub-layer comprising at least one of: aluminum,silver, gold, copper, titanium, chromium, nickel, germanium, indium,tin, platinum, palladium, zinc, aluminum oxide, silver oxide, goldoxide, copper oxide, titanium oxide, chromium oxide, nickel oxide,germanium oxide, indium oxide, tin oxide, platinum oxide, palladiumoxide, zinc oxide, aluminum nitride, silver nitride, gold nitride,copper nitride, titanium nitride, chromium nitride, nickel nitride,germanium nitride, indium nitride, tin nitride, platinum nitride,palladium nitride, zinc nitride, aluminum fluoride, silver fluoride,gold fluoride, copper fluoride, titanium fluoride, chromium fluoride,nickel fluoride, germanium fluoride, indium fluoride, tin fluoride,platinum fluoride, palladium fluoride, or zinc fluoride.
 3. Thewaveguide of claim 1, wherein: the out-coupled light beams converge fromthe first surface to form an upright cone of light and then diverge toform an inverted cone of light above the upright cone of light; and across-section of the upright or inverted cone parallel to the firstsurface comprises an array of dots corresponding to the out-coupledlight beams.
 4. The waveguide of claim 1, wherein: the out-coupled lightbeams diverge from the first surface to form an inverted cone of light;and a cross-section of the inverted cone parallel to the first surfacecomprises an array of dots corresponding to the out-coupled light beams.5. The waveguide of claim 1, wherein: the second surface is in an x-yplane; the in-coupled light beam propagates inside the waveguidesubstantially along the x-direction of the x-y plane; the out-coupledlight beams propagate substantially along a z-direction normal to thex-y plane; the first grating structures are distributed in the x-y planewith respect to corresponding (x, y) positions; the first gratingstructure is each associated with a grating depth, a duty cycle, aperiod, and an orientation in the x-y plane with respect to thez-direction; the first grating structures at different x-directionpositions have at least one of different grating depths or differentgrating duty cycles; the first grating structures at differentx-direction positions have different periods; and the first gratingstructures at different y-direction positions have differentorientations.
 6. The waveguide of claim 1, further comprising anelongated third surface, wherein: a light source couples light into thewaveguide via the third surface to form the in-coupled light beam; andthe light from the light source is collimated into a line shapecorresponding to the elongated third surface.
 7. The waveguide of claim1, wherein: a prism is disposed on at least one of the first surface orthe second surface; and a light source couples light into the waveguidevia the prism to form the in-coupled light beam.
 8. The waveguide ofclaim 1, further comprising a second plurality of grating structures onat least one of the first surface or the second surface, wherein: alight source couples light into the waveguide via the second pluralityof grating structures to form the in-coupled light beam.
 9. Thewaveguide of claim 1, wherein the waveguide further comprises alight-absorbing material layer parallel to the second surface andseparated by a gap from the second surface.
 10. A light projectingsystem, comprising: a waveguide comprising a first surface and a secondsurface, the second surface comprising a first plurality of gratingstructures, wherein the waveguide is a planar waveguide and the firstsurface and the second surface are parallel to each other and are thelargest surfaces of the waveguide; and a light source coupling lightinto the waveguide to form an in-coupled light beam, wherein: thewaveguide is configured to guide the in-coupled light beam to undergototal internal reflection between the first surface and the secondsurface; the grating structures are configured to disrupt the totalinternal reflection to cause at least a portion of the in-coupled lightbeam to couple out of the waveguide from the first surface, the portionof the in-coupled light beam coupled out of the waveguide formingout-coupled light beams; and the waveguide further comprises areflective layer disposed on the second surface and covering the firstgrating structures.
 11. The light projecting system of claim 10,wherein: the reflective layer comprises one or more sub-layers, eachsub-layer comprising at least one of: aluminum, silver, gold, copper,titanium, chromium, nickel, germanium, indium, tin, platinum, palladium,zinc, aluminum oxide, silver oxide, gold oxide, copper oxide, titaniumoxide, chromium oxide, nickel oxide, germanium oxide, indium oxide, tinoxide, platinum oxide, palladium oxide, zinc oxide, aluminum nitride,silver nitride, gold nitride, copper nitride, titanium nitride, chromiumnitride, nickel nitride, germanium nitride, indium nitride, tin nitride,platinum nitride, palladium nitride, zinc nitride, aluminum fluoride,silver fluoride, gold fluoride, copper fluoride, titanium fluoride,chromium fluoride, nickel fluoride, germanium fluoride, indium fluoride,tin fluoride, platinum fluoride, palladium fluoride, or zinc fluoride.12. The light projecting system of claim 10, wherein: the out-coupledlight beams converge from the first surface to form an upright cone oflight and then diverge to form an inverted cone of light above theupright cone of light; and a cross-section of the upright or invertedcone parallel to the first surface comprises an array of dotscorresponding to the out-coupled light beams.
 13. The light projectingsystem of claim 10, wherein: the out-coupled light beams diverge fromthe first surface to form an inverted cone of light; and a cross-sectionof the inverted cone parallel to the first surface comprises an array ofdots corresponding to the out-coupled light beams.
 14. The lightprojecting system of claim 10, wherein: the second surface is in an x-yplane; the in-coupled light beam propagates inside the waveguidesubstantially along the x-direction of the x-y plane; the out-coupledlight beams propagate substantially along a z-direction normal to thex-y plane; the first grating structures are distributed in the x-y planewith respect to corresponding (x, y) positions; the first gratingstructure is each associated with a grating depth, a duty cycle, aperiod, and an orientation in the x-y plane with respect to thez-direction; the first grating structures at different x-directionpositions have at least one of different grating depths or differentgrating duty cycles; the first grating structures at differentx-direction positions have different periods; and the first gratingstructures at different y-direction positions have differentorientations.
 15. The light projecting system of claim 10, wherein: thewaveguide further comprises an elongated third surface; a light sourcecouples light into the waveguide via the third surface to form thein-coupled light beam; and the light from the light source is collimatedinto a line shape corresponding to the elongated third surface.
 16. Thelight projecting system of claim 10, wherein: a prism is disposed on atleast one of the first surface or the second surface; and a light sourcecouples light into the waveguide via the prism to form the in-coupledlight beam.
 17. The light projecting system of claim 10, wherein: thewaveguide further comprises a second plurality of grating structures onat least one of the first surface or the second surface; and a lightsource couples light into the waveguide via the second plurality ofgrating structures to form the in-coupled light beam.
 18. The lightprojecting system of claim 10, wherein the waveguide further comprises alight-absorbing material layer parallel to the second surface andseparated by a gap from the second surface.
 19. The light projectingsystem of claim 10, further comprising: a detector configured to receivereflections of the out-coupled beams off multiple locations on a distantobject to determine distances of the multiple locations relative to thelight projecting system.
 20. A light projecting system, comprising: awaveguide comprising a first surface and a second surface; and one ormore lenses disposed above the first surface, wherein: the secondsurface comprises a first plurality of grating structures; the waveguideis configured to guide an in-coupled light beam to undergo totalinternal reflection between the first surface and the second surface;the grating structures are configured to disrupt the total internalreflection to cause at least a portion of the in-coupled light beam tocouple out of the waveguide from the first surface, the portion of thein-coupled light beam coupled out of the waveguide forming out-coupledlight beams; the second surface is in an x-y plane; the in-coupled lightbeam propagates inside the waveguide substantially along the x-directionof the x-y plane; the out-coupled light beams propagate substantiallyalong a z-direction normal to the x-y plane; the first gratingstructures are distributed in the x-y plane with respect tocorresponding (x, y) positions; the first grating structure is eachassociated with a grating depth, a duty cycle, a period, and anorientation in the x-y plane with respect to the z-direction; the firstgrating structures at different x-direction positions have at least oneof different grating depths or different grating duty cycles; the firstgrating structures at different x-direction positions have differentperiods; the first grating structures at different y-direction positionshave different orientations; the waveguide further comprises areflective layer disposed on the second surface and covering the firstgrating structures; and the one or more lenses are configured to receiveand collimate the out-coupled beams and project the out-coupled beamsinto an environment.
 21. The light projecting system of claim 20,wherein: the reflective layer comprises one or more sub-layers, eachsub-layer comprising at least one of: aluminum, silver, gold, copper,titanium, chromium, nickel, germanium, indium, tin, platinum, palladium,zinc, aluminum oxide, silver oxide, gold oxide, copper oxide, titaniumoxide, chromium oxide, nickel oxide, germanium oxide, indium oxide, tinoxide, platinum oxide, palladium oxide, zinc oxide, aluminum nitride,silver nitride, gold nitride, copper nitride, titanium nitride, chromiumnitride, nickel nitride, germanium nitride, indium nitride, tin nitride,platinum nitride, palladium nitride, zinc nitride, aluminum fluoride,silver fluoride, gold fluoride, copper fluoride, titanium fluoride,chromium fluoride, nickel fluoride, germanium fluoride, indium fluoride,tin fluoride, platinum fluoride, palladium fluoride, or zinc fluoride.22. The light projecting system of claim 20, wherein: the out-coupledlight beams converge from the first surface to form an upright cone oflight and then diverge to form an inverted cone of light above theupright cone of light; and a cross-section of the upright or invertedcone parallel to the first surface comprises an array of dotscorresponding to the out-coupled light beams.
 23. The light projectingsystem of claim 20, wherein: the out-coupled light beams diverge fromthe first surface to form an inverted cone of light; and a cross-sectionof the inverted cone parallel to the first surface comprises an array ofdots corresponding to the out-coupled light beams.
 24. The lightprojecting system of claim 20, wherein: the waveguide is a planarwaveguide; the first surface and the second surface are parallel to eachother and are the largest surfaces of the waveguide; and the out-coupledlight beams couple out of the waveguide from the first surface.
 25. Thelight projecting system of claim 20, wherein: the waveguide furthercomprises an elongated third surface; a light source couples light intothe waveguide via the third surface to form the in-coupled light beam;and the light from the light source is collimated into a line shapecorresponding to the elongated third surface.
 26. The light projectingsystem of claim 20, wherein: a prism is disposed on at least one of thefirst surface or the second surface; and a light source couples lightinto the waveguide via the prism to form the in-coupled light beam. 27.The light projecting system of claim 20, wherein: the waveguide furthercomprises a second plurality of grating structures on at least one ofthe first surface or the second surface; and a light source coupleslight into the waveguide via the second plurality of grating structuresto form the in-coupled light beam.